Category Archives: aircraft engine maintenance

The squirrels in our front yard are gathering pecans, acorns, hackberrys, canned peanuts, potatoes, oranges, etc. You think I’m safe in predicting a rough winter? They’re getting ready. I would like to offer some tips for helping you get ready.

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Sometimes things happen! It’s not very profound, but it is very true. Engines suffer through prop strikes, wire strikes, hot starts and hard landings. Frequently, post incident inspections reveal minor damage and the engines are repaired and returned to service promptly. Recently, engines have been brought to Covington for investigation because “things” have happened to them. One was a reported incident of a starter/generator arcing. The starter/generator malfunctioned and was replaced. While the maintenance appears to have been performed properly, “things” still happen. Here is what we found upon disassembly:

An indication of electrical discharge was noted from the starter gear and all through the accessory gearbox. The #1 bearing failed, which in turn allowed the compressor to shift causing a severe rub of the compressor components and the compressor turbine blades. Another engine suffered from oil starvation:

Another engine suffered from oil starvation:

And a third engine had a failure in the turbine area:

Even though the engines pictured here suffered from in-flight shutdowns, all of the aircraft were able to land safely and all pilots walked away.

Although we understand that “things” happen, we don’t want them to happen to you. If they do, we will work with you no matter where your previous maintenance was done, to ensure that you have a rental/replacement engine as quickly as possible to keep you flying. Remember to be aware of changes in your engine or events that could cause damage. Pay attention to the way it sounds (blade rubbing), looks (metal or debris in oil), smells (oil burning) and feels (vibrations) along with watching the gages. You may be able to detect a problem before some ”thing” happens to your engine.

Need to have a certified expert look at your PT6A engine? Founded in 1972, Covington Aircraft is a world-leading aircraft engine maintenance, repair and overhaul facility specializing in the PT6A turbine engine and R-985 and R-1340 radial engines. We are a Pratt & Whitney Canada certified Distributor and Designated Overhaul Facility (DDOF), and provide world-class corporate and agricultural aircraft service.

It has been amazing to see the engine log books for both the R-985 and R-1340 engine cores coming back to us for overhaul with not one entry reflecting the visual inspections called for in Airworthiness Directive 78-08-07 (R-985-SB 1785) and AD # 99-11-02 (R-1340-SB 1787)!

The service bulletins outline an Ultrasonic inspection of the 985 cylinder heads and Florescent Penetrant inspection of the 1340 heads that must be done at each overhaul. However, there are instructions for visual inspections to be done on the cylinder heads of both engines at specific intervals! The AD Note 78-08-07 (985) stipulates visual inspection of the heads on a 150 hour interval while AD 99-11-02 (1340) states inspections must be done on a 100 hour basis!

The AD notes state the inspections must be done in accordance with the SB’s. SB 1785 which reads as follows: REASON FOR BULLETIN: (2) Provide instruction for visual inspection, at each periodic maintenance interval. The 1340 SB reads: REASON FOR BULLETIN: 3. Provide instructions for inspection of cylinder heads at periodic maintenance.

You are looking for cracks in the aluminum head that are evidenced by jet-black combustion residue deposited at the root area between two fins in the designated areas. The coloration will not be visible in areas that aren’t cracked and leaking combustion residue. It is possible for oil leaks to burn onto the cylinder cooling fins but that is usually dark brown colored and typically involves a larger portion of the head. Combustion residue is dark black and may be oily and gritty feeling. I have included a couple of scanned illustrations showing the areas of the head identified in the bulletins:

The pictures seem to indicate that the 1340 head doesn’t experience cracking around the side of the head and that the 985 doesn’t crack across the top. However, cylinders of both the R-985 and R-1340 engine can develop cracks in either location on the heads!

Some careful reviews of the requirements are in order due to the confusing wording of the AD notes vs SB’s!

R-985: The AD affecting the 985 states: “To prevent cylinder head separation from the barrel, perform the following in accordance with Pratt & Whitney Aircraft Service Bulletin No. 1785 or later FAA-approved revision.” (Paragraph) 1. “Visually inspect cylinder heads in accordance with Part B of the bulletin as follows: (Sub-paragraph) B. “Cylinders Ultrasonically inspected, inspect within 150 hours time in service after effective date of the AD, and thereafter at intervals not to exceed 150 hours time in service.”

Service Bulletin 1785 references the R-985 Wasp Jr. Engine Maintenance Manual, Part No. 118611; Periodic Inspection. That inspection table places the check of the rear of the cylinder head for cracks or evidence of exhaust gas leakage in column “B”; 100 hours! To correctly comply with the AD the 985 cylinder heads must be visually inspected on a 100 hour basis!

R-1340: The 1340 AD and Service Bulletin are no less confusing! The AD instructs the mechanic to inspect the cylinders in accordance with SB 1787 dated September 07, 1983. However, the AD states that cowled and baffled installations should have an initial inspection at 125 hours and subsequent inspections at 250 hour time in service since last inspection. All other installations (translates “Cropdusters”) are to have an initial inspection at 50 hours and subsequent inspections at 100 hours! The SB allows for cowled and baffled engines to be inspected at 500 hours and un-baffled or “cropduster” type installations at 200 hour intervals. Sadly, the AD note is the law! You get to inspect using the technique given in the respective SB and accomplish the inspection at the intervals specified in the AD! Oh well, what do you want? Good looks and money too!

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It’s annual inspection season again. I guess it like death and taxes…sure to come around. Lots of folks have asked “what should I have done to my engine during the annual?” The engine maintenance manual, part number 118611 contains the Periodic Inspection Tables listing the Requirements for the “A” (50 hr), “B” (100 hour inspection), “C” (200 hour) and “D” (Midway to Overhaul) inspections on R1340 and R985 engines. Of the requirements listed I’d like to offer some recommendations on seven of the “heavyweights”.

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The customer had sent in an exchange set of fuel nozzles at his normal change interval of 300 hours. The nozzle set appeared to be reasonably typical in appearance; however, every one of the nozzles exhibited streaking during the spray check as received! Nine of the nozzles cleaned up during the cleaning process and spray checked ok. Five nozzle tips had to be replaced to be able to return the set to service. This was unusual for this operator, and he sought for ideas as to what might be the problem.